1. Field of the Invention
The present invention relates to a vehicle wheel aligner which comprises sensors that are mountable to the wheels of a vehicle and generate signals representative of the orientations of the wheels. More particularly, the invention relates to an apparatus and method for automatically calibrating the sensors during the normal operation of the wheel aligner.
2. Description of Related Art
Vehicle wheel aligners are well known in the art. Such aligners typically comprise four alignment heads which are mountable on the vehicle wheels and include sensors for generating signals representative of the angular orientations of the wheels. Typically, separate sensors are provided for measuring the angles of each wheel in the toe, camber, and caster planes. Angles in the toe plane are commonly measured using either electromechanical string-type angle measuring instruments, such as is disclosed in U.S. Pat. No. 4,341,021 issued to Beissbarth, or opto-electrical angle measuring instruments, such as is disclosed in U.S. Pat. No. 4,761,749 issued to Titsworth et al. Angles in the camber and caster planes may be measured using inclinometers, which are known to those in the art.
One problem with vehicle wheel aligners is that, during the course of their usage, the sensors may become out of calibration. Unless the sensors are calibrated regularly, the out-of-calibration condition can exist for some time, thereby causing improper wheel alignment settings. However, alignment technicians are often not comfortable performing the calibration process, and the process itself takes away from the productive use of the wheel aligner.